Everyone's estate - whatever its size - needs care in planning

Anyone who owns anything at all has an estate. That very basic fact is often ignored by those who say that they do not have assets enough to worry about and that, anyway, whatever there is will go eventually to a surviving spouse or to children.

Carelessness in estate planning can be serious, no matter how little or how much is involved. It is important at all ages, and it becomes more so in the years before retirement. Without planning, federal and state taxes can erode estates carefully accumulated through the years.

And without planning, through the drafting of wills, what is left may be distributed in ways you did not intend. Do not assume that a spouse will automatically receive an estate intact; unless there is a valid will, the estate may be divided according to the laws of the state that has jurisdiction.

Planning is important at any time, but it is particularly so now when, because of inflation, assets must be conserved.

An individual's estate consists of valuable assets accumulated in a variety of ways. These include life insurance, bank and savings accounts, money in savings-and-loan associations and credit unions, stocks, bonds (including Series E and other issues), pension and profit-sharing plans, real estate, business and professional interests, personal property - in fact, anything and everything of any value. For the purpose of taxation a ''gross estate'' includes all assets an indiviudal owns at the time of death, or will receive then, and any gifts made in contemplation of death. A ''taxable estate'' is the gross amount less liabilities.

Everyone should have a sound estimate of his or her estate; lacking one can mean long delays in distributing assets. Keep in mind that federal and state tax collectors often have a less modest opinion of the value of your estate: Be realistic.

Probably the most important point in planning estates is the need for drafting wills; both husbands and wives should have wills, written instruments executed with the formalities prescribed by law, in which the distribution of assets is specifically directed. An administrator is bound to follow the provisions of a will - and the individual making the will can name the administrator.

Through the will, an individual can make an outright disposition of assets, or the individual can create a ''trust'' by transferring all of a part of the estate to a trustee.

Under a trust arrangement, the maker can receive income from the trust during his or her lifetime, with the principal to be disposed of later. A ''testamentary trust'' effective after death can ensure continuing income for a spouse or dependent.

Trusts should be created with the help of lawyers, financial advisers, or other experts who will see that provisions of laws are met and that all possible benefits - largely tax savings - are written into them.

In estate-tax areas, planning should consider such things as federal estate gift and tax laws, and possibly state laws, savings that may be possible through marital deductions, joint tenancies, and other legal arrangements.

The goal should be to keep as much as possible for yourself and for those you would like to receive maximum benefits from your estate. This is not a matter of chiseling on taxes, but of making proper and legal use of provisions that Congress wrote into tax laws to benefit taxpayers.

Some of the things an adviser might suggest you do under federal estate and gift regulations:

* You can give as much as you like to your spouse before death or through a will without incurring a gift or estate tax.

* You can now give up to $10,000 a year ($20,000 if your spouse joins in the gift) to each of as many people as you wish without incurring a gift tax.

* You can put money into life insurance or some other investment that has no way of directly benefiting you.

* You can keep some of your assets in separate, rather than joint, ownership; that is, you can arbitrarily decide that 50 percent of your assets should be in your name, 50 percent in your spouse's name. If either passes on, only half the estate would be involved.

Under 1981 tax laws, a much more generous tax credit increases the amount that can be given away or be bequeathed tax-free. The amount will rise to $325, 000 in 1984 and continue climbing until it reaches $600,000 in 1987 and thereafter.

Federal laws set the unified estate- and gift-tax rate schedule, with progressive rates based on cumulative transfers during lifetime and death. The maximum federal rate, 60 percent this year, will be reduced to 55 percent in 1984, then 50 percent in 1985 and later years. Only the very rich pay the maximum.

Marital deductions are allowed without limit under current law, so an entire estate can be passed along to a spouse without a federal tax burden. To qualify, it is necessary to pass an estate along outright to a spouse through a will, to hold the estate in joint ownership, or to use some other legal arrangement to designate him or her as having ''control'' over the estate.

Gift and estate-tax savings are also possible through what is known as joint tenancy with right-of-survival arrangements by two or more people, by which the assets owned by the first who passes on automatically passes to the others.

There are provisions in these and other tax-saving arrangements that are often complex and can be subject to changes. Using them, it is now possible to avoid federal estate and gift taxes entirely. It is wise, however, to avoid potential legal and tax problems by consulting a lawyer or tax expert. The cost of getting help is likely to be greatly outweighed by the savings from expert advice.